This invention relates to a magnetic recording medium for recording information on and reproducing information from the magnetic recording medium, such as a magnetic disk.
FIG. 1 is a perspective view showing the relationship between the magnetic head and the magnetic recording medium in a conventional magnetic recording device shown, for example, in "Theory of Magnetic Recording" by Masaaki Nishlkawa, published by Kabushiki Kalsha Asakura Shoten, November 1985; Drawing No. 1.2. FIG. 2 and FIG. 3 are schematic diagrams showing the principle of recording and the principle of reproduction in the magnetic recording device of FIG. 1. In the figures, a magnetic head 4 comprises a core 1 with a gap S and a coil 2 wound on the core 1. A magnetic recording medium 5 is moved relative to the magnetic head 4 in the direction indicated by arrow D. An electrical circuit 6 is for passing a write current I through the coil 2 to record information, and reproducing information from the read voltage derived from the coil 2. Information is written on the magnetic recording medium 5 along a track.
The principle of recording information on the magnetic recording medium 5 will now be described with reference to FIG. 2. The magnetic recording medium 5 is moved relative to the magnetic head 4 in the direction D In FIG. 2. An alternating current I is made to flow from the electric circuit 6 through the coil 2 In accordance with the Information to be recorded. The coil 2 and the core 1 generates an alternating magnetic field (magnetic flux) F in the core 1 in compliance with the alternating current I. The alternating magnetic field F leaks at the gap 3 and reaches the magnetic recording medium 5. The magnetic recording medium 5 is magnetized into the direction indicated by arrow M in FIG. 2 responsive to the alternating magnetic field F that leaks at the gap 3. Thus, information is recorded on the magnetic recording medium 5.
The principle of reproducing information from the magnetic recording medium 5 will now be described with reference to FIG. 3. As shown in FIG. 3, part of the magnetic flux F emanated from the magnetic recording medium 5 enters the core 1 and interlinks the coil 2. When the magnetic recording medium 5 is moved in the direction D in FIG. 3, the magnetic flux F interlinking the coil 2 varies over time, and a voltage is therefore induced in the coil 2 in accordance with the Faraday's law. When the magnetic head 4 passes the part of the magnetic recording medium 5 where the magnetization is reversed, the variation of the magnetic flux F interlinking the coil 2 becomes the maximum, so that the voltage induced in the coil 2 becomes the maximum. By detecting the position of the maximum voltage through electrical processing in the electrical circuit 6, the position of reversal of the magnetization on the magnetic recording medium 5 is known, and information is reproduced from the magnetic recording medium 5.
When the amount of information to be recorded and reproduced is increased and it is required that magnetization be made more densely on the magnetic recording medium 5, the reproduction output is lowered due to demagnetization effect, with the result that reliability of the magnetic recording device is lowered.
This will be explained with reference to FIG. 4A and FIG. 4B, which illustrate the demagnetization effect associated with the magnetic recording device of FIG. 1. FIG. 4A shows the magnitude of the alternating magnetic field F leaking at the gap 3 during recording against the position on the magnetic recording medium 5. FIG. 4B shows the magnitude of the magnetization at the part of the reversal of magnetization on the magnetic recording medium 5 against the position on the magnetic recording medium 5.
For recording information, an alternating magnetic field F with the width of reversal being zero (i.e., which varies stepwise) as shown in FIG. 4A is generated, so that the magnetization shown in FIG. 4B should also have a zero width of reversal. However, because of polarization magnetic charge appearing in the region of reversal of magnetization, demagnetizing magnetic field F is generated in front of and at the back of the position of reversal of magnetization, tending to expand the width of reversal of magnetization. The width of reversal of magnetization is therefore expanded self-consistently. When the interval of reversal of magnetization on the magnetic recording medium 5 is long, the increase in the width of reversal of magnetization is negligible. When the interval of reversal of magnetization is short, the effect cannot be neglected. As a result, error in the reading of the position of the reversal of magnetization on the magnetic recording medium 5 may occur, and the reliability of the magnetic recording device is lowered.